ape: fix name clash, have to use _SLEEP syscall instead of ape sleep in plan9 code (thanks jamos)

this fixes etimer() from ape built libdraw as posix sleep() uses
seconds while plan9 uses miliseconds.

sys/src/ape/lib/9/libc.h

@@ -150,6 +150,7 @@ extern	vlong	_NSEC(void);
 #define mallocz _MALLOCZ
 #define nsec	_NSEC
 #define iounit	_IOUNIT
+#define sleep	_SLEEP
 
 #define getwd(buf,len)	getcwd(buf,len)
 #define postnote(who,pid,note)	kill(pid,SIGTERM)